Ancient underground streams of heated rock, called a mantle plume, might be an explanation for the instability of Antarctica’s western ice sheet, according to a new NASA study.

Scientists have been debating whether or not mantle plume heat contributes to western Antarctica’s instability. Some recent studies provided evidence this might be the case, but even this study’s authors were skeptical.

“I thought it was crazy,” Hélène Seroussi, the study’s co-author and scientist at NASA’s Jet Propulsion Laboratory, said in a release.

“I didn’t see how we could have that amount of heat and still have ice on top of it,” Seroussi said in a statement.